In image-guided operations, it is necessary to provide objects such as bones or medical instruments with marker devices. A marker device consists for example of one or more reflective spheres which can be detected by sensors. The position of the marker device and therefore the position of the object can be determined from the position of the spheres with respect to each other.
One commercially available device for fastening a marker device to a bone consists of a screw, a clamping device, an adjusting screw and a sleeve which comprises a mounting for the marker device. When attaching the device, the screw is initially screwed into the bone, and the sleeve together with the adjusting screw and the clamping device is then fitted onto the screw. The clamping device is then fixed relative to the screw, and the sleeve is pressed against the bone in the desired alignment by means of the adjusting screw and thus fixed.
One of the disadvantages of this fastening device is that attaching it to the bone requires a large number of steps working on the patient and thus increases the length of time which the patient has to spend in the operating theatre.